On Nov 3, 2010, at 10:12 AM, jimlux wrote: > Bob Camp wrote: >> Hi >> I have indeed seen people try to do this with 18 ~ 24" aperture optics. They >> don't seem to do a lot better than the smaller stuff spotting holes at >> distance. They do get a nice bright image though. Bob >> > > Yeah, at that size, the atmospheric propagation issues are probably the > limiting aspect. For astronomical use, you tend to be looking closer to > straight up, which helps (same for looking down). >
Looking down is typically better than looking up; the disturbing parts of the atmosphere are further away. > Clearly (a pun) it is possible to get this kind of performance from > reasonable sized optics e.g. the proverbial reading license plates from > orbit... 10cm resolution at 300 km range.. .1/3E5 -- .3 microrad (I do > calculations in my head MUCH better in metric)... even 1 meter resolution > (which is widely published) from orbit is 3 microradian. > > the KH series satellites are rumored to have 2.4 meter optics. Whether they > have 10 cm resolution in use is uncertain. > The HiRise camera on the Mars Reconnaissance Orbiter has a 0.5 meter aperture and routinely does 20 cm / pixel resolution from orbit. http://photojournal.jpl.nasa.gov/catalog/PIA07087 http://hirise.lpl.arizona.edu/teknikos.php Regards Marshall > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
